For me, it's impossible US Dollar would crashes. Even if it crashes, other currency will take over US Dollar place, like Euro or Yuan.
I don't think bitcoin could replace it.
Fiat will just be replace by fiat also,when the dollar crashes most likely the euro will replace it as the top fiat currency in the world.
The chance is already small that it can crash and that is because you also can see now that there are now more people that is going to have Bitcoin.
But there are still a lot of people that dont even knows how Bitcoin works and that is the problem, so you have to promote it more.